1. Technical Field
The present invention relates to a line head, an image forming apparatus and an image forming method.
2. Related Art
In an image forming apparatus using an electrophotographic method, such as a copier or a printer, an exposure unit for exposing the outer surface of a rotating photosensitive body and forming an electrostatic latent image is included. As for such an exposure unit, a line head having a structure in which a plurality of light emitting devices is arranged in a rotation axis direction of the photosensitive body is known (for example, see JP-A-59-38079).
For example, in the line head disclosed in JP-A-59-38079, the plurality of Light Emitting Diodes (LEDs) is arranged in a row and the plurality of LEDs is modularized by a predetermined number. In addition, in such a line head, the plurality of LEDs sequentially is lit up for every module.
In such a line head, since the plurality of LEDs sequentially is lit up for every module, the switching timing of lighting each module should be set in consideration of the rotation velocity (circumferential velocity) of the photosensitive body. A slight error occurs in such switching timing and this error has an adverse influence on the quality of a latent image which finally is obtained. In particular, the influence of such an error on the quality of the latent image which finally is obtained is increased if a plurality of rows of the LEDs arranged in a main scanning direction is arranged in a sub scanning direction.
It is preferable that the number of signal lines for controlling lighting of the LEDs is as small as possible. Accordingly, it is possible to prevent or suppress noise from being mixed from such lines and realize a high-accuracy exposure process.